Transcript for 'Fat Letters' Have Young Kids Worried About Their Weight

Up next, students call them fat letters. But reports that a growing number of schools are sending home to parents, indicating whether kids are making the grade when it comes to bmi, the body mass index. Are they hurting more than they're helping? Abc's bianna golodryga takes a closer look. Reporter: Middle schooler, lucy williams, has multiple report cards to worry about. The one concerning her academic grades. And this one, concerns her weight. I'm insecure because I'm taller than a lot of girls in my school. And I'm also bigger than a lot of them. And not incredibly skinny. Reporter: The fitness gram is part of a growing initiative to track students body mass indexes OR BMIs. Students take part measuring students at annual weigh-ins. Then, sending reports home to parents. Indicating whether a child is in the green healthy zone, or in the red danger zone. Pediatricians say bmi readings are helpful in combatting childhood obesity. Right now, it's the best measurement we have to determine if a child's weight is healthy or unhealthy. Reporter: But industry experts say the readings do more harm than good. For children that are insecure about their weight, these tests can trigger an eating disorder. Reporter: As many as 60% of all 6-year-olds to 12-year-olds are worried about their weight. We asked lucy and six other girls to weigh in on school bmi reports. I know all of your schools have a bmi reading now. How do you feel about them? I hate them. It doesn't do much for people except make them more insecure about themselves. Reporter: The girls' mothers are also concerned. When they are entering adolescence, their bodies are changing. And they get this number that says, you know, you're not the right number. It's just a horrible way to start womanhood. There's so much stress. The last thing they need is the school to step in, you're too skinny. You're too fat. Reporter: For "good morning america," bianna golodryga, abc news, new york. A lot of discussion here. We're going to bring in abc news senior medical contributor, jennifer ashton. Tell us what you saw? To look at both sides, i believe it's well-intentioned, right? We know that 30% of children or more are overweight or obese. And the idea is to target an environment where they spend 60% of their time. However, the flipside is, how is this information going to help? And will it do harm? When you're talking about kids, peer pressure, stigma, self-esteem. Those are not good things for an average child. When you talk about a child already dealing with a weight issue, can be compounded. What can parents do constructively to work with them? That's the key. How will parents and the school districts utilize this information? We have to understand that when you're talking about body mass index, the flip side of this curve is just as unhealthy as being overweight. And then, education is key. You want to bring in nutritionists. Bring in sports physiologists. Bring in doctors who can help the factlies deal with this information. If you have a child that is obese, you know that child is obese. Is there a way to do that not to tie it to -- what feels like a school activity. When you consider school districts and the food they're eating in the schools may be contributing. We don't have phys-ed now. We need to hold ourselves accountable to the same criteria. We need to be exercising an hour a day. And that needs to start at school, by not removing phys-ed, as you said, sam. We need to get rid of the junk food machines in almost every school. And the bmi is not perfect. It can overestimate someone's obesity. It's not a great measure. Right now, it's all we have. But this is something that parents can opt out of, by the way. But it's very controversial. It's tough to see the kids say how much they hated it. Difficult. Coming up here, the ultimate

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